Serial flash memory support

Serial flash memory support

[Hinko Kocevar]

Hi everybody,

I'm starting to code kernel driver for SPI serial flash memory (we are using 
M25Pxx chips from ST). In the end I would like to see this chip to hold jffs2 
fs and be mtd-compatible. After quick inspection of current CVS code I didn't 
find any code in there for SPI flash. So my questions are:

Has anybody done something on the SPI flash memory devices already?

If I start to implement mtd driver for this chip what functions do I need?

I've glimpsed over the mtd_info struct which contains lots of function pointers 
- are they all necessary?

regards,
hinko k

-- 
..because under Linux "if something is possible in principle,
then it is already implemented or somebody is working on it".

					--LKI

Re: Serial flash memory support

[Andrew Victor]

hi Hinko,

> Has anybody done something on the SPI flash memory devices already?

Yes, there is a driver for Atmel's DataFlash.

The driver is included in the 2.4 ARM-Linux kernels
(www.arm.linux.org.uk) and the 2.6 patches for the AT91RM9200 processor
(http://maxim.org.za/AT91RM9200/2.6/).


Regards,
  Andrew Victor

Re: Serial flash memory support

[Hinko Kocevar]

Andrew Victor wrote:
> hi Hinko,
> 
> 
>>Has anybody done something on the SPI flash memory devices already?
> 
> 
> Yes, there is a driver for Atmel's DataFlash.
> 

ST serial flash seems pretty close according to the specs.

> The driver is included in the 2.4 ARM-Linux kernels
> (www.arm.linux.org.uk) and the 2.6 patches for the AT91RM9200 processor
> (http://maxim.org.za/AT91RM9200/2.6/).
> 

Great, 2.6 patch looks promising. Thank you. Can you provide information about 
timings for accessing SPI serial flash. As I could see from kernel boot dump on 
the maxim.org.za page you seem to be using SPI serial flash for code and data.

Our application has user data on the SPI serial flash and at boot time its 
contents is read - it has to be done as fast as possible. Is there some fs you 
could recomend for this purpose?



regards,
hinko k

-- 
..because under Linux "if something is possible in principle,
then it is already implemented or somebody is working on it".

					--LKI

Re: Serial flash memory support

[Hinko Kocevar]

Damian Slee wrote:
> Jffs2 does support atmel serial dataflash, as far as the driver for spi,
> that is more hardware dependent.   They recently changed the conditional 
> compiles to be CONFIG_JFFS2_FS_WRITEBUFFER for nand and dataflash.
> 
> BTW JFFS2 takes ages to do the startup scan of the flash with the 528 or
> 1056 block size of the dataflash.

Our serial flash uses 256 byte pages and is forming sectors with them, 
depending on the whole flash size. But I guess that is no case for accessing it 
quicker.

>  I was evalutating the latest cvs JFFS2 last week upon eCos.  I think it
> was about 7 seconds for 64kbytes, with the SPI clocked at 15MHz.

That is too slow for our application.
My conclusion would be that JFFS2 is too much for 'slow' SPI serial flash. I 
guess will just use raw access to the data stored there and achieve maximum 
speed. Can mtd raw access driver/module be used for this purpose or is that 
driver meant for a another stuff?

regards,
hinko k
-- 
..because under Linux "if something is possible in principle,
then it is already implemented or somebody is working on it".

					--LKI